Unfortunately with car rental you often find yourself in a situation when  you pick a car at a favorable rate and drive happily until turns into a check with twice the rate when you return the car to the rental office. That is a common practice of rental companies to increase your deal by little extras here and there. They would advertise low rental fees and adding a lot of extra hidden fees on top, which can sometimes push the final rates twice as high and even higher. SO to avoid overpaying for car rental due to extra fees it's highly recommended to look out for the following little extras that car rental companies may throw into the rental contract:

Insurance

Insurance is one of the most common methods car insurance companies utilize for making you pay more. And in some states or countries it's hard to avoid it, since certain insurance waivers are mandatory for rental cars. Sure, you can try to use own insurance policy or credit card to pay for the potential liability, but you will have to check with your provider first. And this may be very challenging when going overseas, so you will be forced to get insurance for an extra fee.

Not-full tank

Most car rental companies will add an extra fee if you return the car with a not-full tank, even if you've initially rented it without a full tank. Some companies offer full tank options that allow you to avoid the extra fuel fees, but their per-gallon prices may differ from those you would actually find at local gas stations.

Full days and early return

It is very important to remember that all car rental companies have 24-hour days. So if you take a car on Monday morning and return it on Tuesday evening, this will count for two full days. In case you don't want to pay for two full days, you may want to look for car rental companies that also feature hourly fees. But such rates are always higher than daily or weekly rates, so you may end up saving little or no money at all.

Returning a car earlier than intended may seem like a good idea, but most car rental companies will charge you extra for doing so. If you've booked a car for a particular period but returned it earlier, there may be extra fees or you may be reimbursed the difference with the interest taken out.

Age restrictions

Most car rental companies will charge extra if the driver is younger than 25. Even higher rates will apply for drivers aged 21 or younger. Senior drivers who are older than 70 years old will also get special fees, if the rental company will generally accept their request.

Mileage limits

In most cases, car rental companies have unlimited mileage. However, you should be careful when travelling to a different state or country, as the regulations may differ a lot and you may be charged for driving an excess of miles per day.

Drop-off charges

Dropping off the car at a location different from where you've taken it from will usually result in an extra fee, but this usually depends on the company and where you've actually dropped the car off. Usually, the drop-off rates apply when leaving the car in a different state or country, and depending on the case these may rocket sky-high.

Multiple driver fees

If there's more than a single driver added to the contract, the company may charge an extra fee. However, some car rental companies won't charge extra fees if the second driver is the main driver's spouse or partner.

Additional extras

Car rental companies will offer a wide range of extras that can be rather useful for an additional price. Things like child seats, GPS navigation systems, top racks, entertainment systems, hand controls and more will cost differently depending on company and country, so inquire in advance when booking the car.